3rd generation partnership project (3GPP) long-term evolution (LTE) is a technology for enabling high-speed packet communications. Many schemes have been proposed for the LTE objective including those that aim to reduce user and provider costs, improve service quality, and expand and improve coverage and system capacity. The 3GPP LTE requires reduced cost per bit, increased service availability, flexible use of a frequency band, a simple structure, an open interface, and adequate power consumption of a terminal as an upper-level requirement.
Machine-type communication (MTC) is an important revenue stream for operators and has a huge potential from the operator perspective. There are several industry for a working on an efficient machine-to-machine (M2M) system with some industry members developing a new access technology dedicated for MTC. However, it is more efficient for operators to be able to serve MTC user equipment (UE) using already deployed radio access technology. Therefore it is important for operators to understand whether LTE could be a competitive radio access technology for efficient support of MTC. It is envisaged that MTC UE's will be deployed in huge numbers, large enough to create an eco-system on its own. Lowering the cost of MTC UE's is an important enabler for implementation of the concept of “internet of things”. MTC UE's used for many applications will require low operational power consumption and are expected to communicate with infrequent small burst transmissions. In addition, there is a substantial market for the M2M use cases of devices deployed deep inside buildings which would require coverage enhancement in comparison to the defined LTE cell coverage footprint.
Recently, there has been a surge of interest in supporting proximity-based services (ProSe). Proximity is determined (“a user equipment (UE) is in proximity of another UE”) when given proximity criteria are fulfilled. This new interest is motivated by several factors driven largely by social networking applications, and the crushing data demands on cellular spectrum, much of which is localized traffic, and the under-utilization of uplink frequency bands. 3GPP is targeting the availability of ProSe in LTE rel-12 to enable LTE become a competitive broadband communication technology for public safety networks, used by first responders. Due to the legacy issues and budget constraints, current public safety networks are still mainly based on obsolete 2G technologies while commercial networks are rapidly migrating to LTE. This evolution gap and the desire for enhanced services have led to global attempts to upgrade existing public safety networks. Compared to commercial networks, public safety networks have much more stringent service requirements (e.g., reliability and security) and also require direct communication, especially when cellular coverage fails or is not available. This essential direct mode feature is currently missing in LTE.
When a MTC UE can perform ProSe operations with another UE, in order to avoid waste of battery life of the MTC UE, a method for triggering detach or a power saving mode (PSM) for the MTC UE may be required.